Vitreous enamel coated steel article and method of making the same



Patented Apr. 14, 1942 UNITED STATES PATENT", OFFICE VITREOUS ENAMELCOATED STEEL ARTI- CLE AND METHOD OF MAKING THE SAME Harvey RossBalding, Sharpsville, Pa., and John A. Eckel, Gary, Ind.

' No Drawing. Application October 7, 1939,

Serial No. 298,506

4 Claims. (01-. 29-148) In the manufacture of vitreous enamel coatedsteel articles it is customary to form or draw sheets of steel toproduce the shapes desired and to thereafter apply the vitreous enamelcoatlngs. they are fused orsintered onto the steel articles. At thisstage of the process, numerous difliculties frequently arise.

One of thesedifliculties is reboiling, this causing the formation,during the fusing or sintering of the coatings, of objectionable surfacedefects. This difliculty is commonly believed to be due to bubbles ofgas which are released from the steel when it is heated during thefiring of the coatings. These surface" defects obviously mar theappearance of the finished articles.

Another difliculty frequently encountered is the formation of openingsor depressions in the surfaces of the enamel coatings, these being knownin the art as black specks, copper-heads andfish-scaling. The formationof these defects is not consistent, it apparently varying with thecoating material and the time and temperature to which it is fired,these factors, in turn, differing among the various fabricating plants.I When the steel sheets used to form the articles are cold rolled steel,that is to say, steel heavily reduced by cold working from a hot rolledunfinished product, and when this steel is oxidized or unkilled, it hasbeen found that reboiling difficulties are not generally encounteredduring the firing of vitreous enamel coatings on the articles, with thesame degree of frequency as when the articles are made from steel sheetsof oxidized or unkilled hot rolled steel, this being steel finished byhot rolling methods excepting forvery slight cold rolling necessary 'toimpart its temper.

However, it has been found that this greater freedom from reboilingexhibited by cold rolled oxidized steel depends upon the carbon andmanganese contents of the steel. Thus, it has been found that steelcontaining .07 per cent carbon or more and .30 per cent manganese 'ormore usually is not subject to this difficulty. Steel containing from.04 per cent to .06 per cent carbon and from .20 per cent to .30 percent manganese may or may not be subject to this difficulty, dependingon factors not known at the present time. Steel containing less than .04per cent carbon and'substantially less than .20 per cent manganeseusually causes considerable trouble through reboiling and, if themanganese is These coatings are then heated so that.

In other words, the lower the carbon and manganese contents of oxidizedcold rolled steel, the

, more frequent and objectionable is reboiling durless than .12 percent, the difiiculty is encoun- ,tered to a most objectionable degree.

ing the fusing or sintering of vitreous enamel on an article made of thesteel.

In spite of this greater reboiling tendency of cold rolled oxidizedsteel that is low in its content of carbon and manganese; there is ademand for the same for formation-into products to be vitreous enamelcoated. This is due to the'greater freedom of such steel from warpingduring the firing of the coatings, and its greater softness andductility which aids in deep stamping, spinning and other formingoperations necessary to produce the various shapes.

With the foregoing in mind, the present invention is based on thediscovery that the addition of titanium to molten steel which is cast asan oxidized unkilled steel and processed to cold rolled steel whensolidified, results in a material which when formed into articles thatare coated with vitreous enamel, is not subject to reboilingdifliculties during the firing of the coatings.

It has been discovered that reboiling is positively prevented unless thecarbon content of the steel is less than .03 per cent andthe manganeseis less than .06 per cent (by ladle analysis), and in this latter case,reboiling is so greatly reduced as not to produce appreciably harmfuleffects during firing of the ings on the steel.

The treatment of iron and steel with titanium for other purposes is ofcourse old, butso far as is known, its peculiar efiect in preventing orgreatly reducing reboiling during vitreous envitreous enamel coatamelcoating, when added to steel produced as an oxidized cold rolled steelof low carbon and manganese content, has hitherto been unknown. The

peculiar effect of titanium in preventing reboiling is not, as might bethought, due to its well known deoxidizing power, because aluminum, aneven stronger deoxidizer than titanium,'does not prevent reboiling evenwhen added in excessive amounts. As a matter of fact, the use ofaluminum causes an increase inthe reboiling.tend

ency of cold rolled steel.

Although titanium possesses its peculiar effect 2 same.- Thus, steelanalyzing in' the ladle as' containing from .07 per cent to .03 per centcarbon 2,279, 93; v V i. A method of producing vitreous and from .30 percent to .10 per cent manganese, requires about three pounds per ton ofsteel of the titanium alloy when this alloy contains 20 per 'centtitanium; In such a case, reboiling difficulties are completelyeliminated. On the other hand, three and one-half pounds of such analloy must be. added for each ton of steel containing, when in theladle, .03 per cent maximum carbon and from .06 per cent to .10 per centmanganese. If the carbon is as low as .03 percent maximum, and ifthemanganese content is below .06 per cent, then at least three andone-half pounds of 20 per cent titanium alloy per ton of steel must beused and pref erably five pounds per tonshouldbe used. In the case ofsteel of such extremely low carbon and manganese contents reboilingdifliculties are not entirely eliminated but they are so greatly reducedthat they are no longer productive of material damage to the enamelcoatings.

It is obvious from the above that the amounts of titanium added to steelto be cast without being killed and worked into a cold rolled productthat is formed into articles which are coated with vitreous enamel, mustbe varied in accordance with the carbon and manganese content of thesteel,.if reboiling difliculties during firing of the enamel coatingsare to be prevented.

A further important effect is obtained by the use of the titanium,namely, the formation of defects such as black specks, copper-heads andfish-scaling are retarded or entirely prevented regardless of the slightvariations in enameling practice encountered in the case of the variousfabricating plants.- In other words, the steel is no longer particularlysensitive to plant practices.

It is to be understood that in all cases, the steel will have ananalysis producing an oxidized cold rolled steel suitable for use in themanufacture of vitreous enamel coated steel articles. The steel willdiffer from the prior art' steel provided for this purpose in that itwill contain the titanium and will-be effectively free from r thedifficulties encountered heretofore.

This requires at least .50 pound of'titanium per ton of steel.

We claim:

coated steel. articles, which includes producing oxidized molten steelcontaining less than .0'l$ carbon and less than .30% manganese, addingtitanium thereto in amounts insuiiicient to kill said steel, solidifyingsaid unkilled steel, producing cold rolled steel from said steel when itsolidifies, producing the desired articles from said cold rolled steeland fusing vitreous enamel coatings on said articles.

2. -A method of producing vitreous enamel coated steel articles, whichincludes producing oxidized molten steel containing less than .0"l%carbon and less than .30% manganese, adding titanium thereto in amountsinsufllclent to kill said steel, solidifying said unkilled steel,producing cold rolled steel from said steel when it solidifies,producing the desired articles fromsaid cold rolled steel and fusingvitreous enamel coatings on said articles, said titanium being added tosaid molten steel to the amount of at least .50 pound per ton of saidsteel.

3. A method of producing vitreous enamel coated steel articles, whichincludes producing oxidized molten steel containing less than .0,'7%

carbon and less than .30% manganese, adding titanium thereto in amountsinsuflicient to kill said steel, solidifying said unkilled steel,producing cold rolled steel from said steel when it solidifles,producing the desired articles from said cold rolled steel and fusingvitreous enamel coatings on said articles, said titanium being added tosaid molten steel to the amount of at least .50 pound per ton of saidsteel, and being increased above said amount when the carbon andmanganese contents of said steel are less than said percentagesasrequired to retard or eliminate the formation of defects in saidvitreous enamel coatings fused on said articles.

4. Cold rolled unkilled steel containing less than .07 per cent carbonand less than .30 per cent manganese and being otherwise of an analysissuiting it for working into articles requiring cold forming in theirproduction, said steel containing at least .50 pound per ton of steel oftitanium to materially retard 'reboiling or other similar harmfuleffects when vitreous enamel is fused on its surface.

HARVEY ROSS BELDING.

JOHN A.

